Is swearing by Allah at the time of divorce, by the husband saying to his wife: "By Allah Almighty, if you do that, you are divorced," considered an oath of divorce or an oath by Allah for which there is an expiation for an oath?

A husband's statement, "If you do such and such, you are divorced," is a conditional divorce tied to the aforementioned action, and his oath to that effect is to affirm this condition. If the wife does not perform that action, no divorce occurs. But if she does perform it, then the divorce occurs. This is not considered a breach of an oath by Allah, because a breach only occurs if the divorce does not take place when the action sworn upon is performed.